1. Field of the Invention
The present invention relates to a stage apparatus for driving an object, being suitably used for a stage system of an exposure apparatus that is used for transferring a mask pattern onto a substrate in a photolithography process for manufacturing devices such as semiconductor elements, imaging elements, liquid-crystal display elements, or thin-film magnetic heads and the like.
2. Related Art
In a photolithography process for manufacturing devices such as semiconductor elements or liquid-crystal display elements (electronic devices, micro-devices, and the like), in order to project and expose via a projection optical system a circuit pattern formed on a reticle (or photomask) onto a wafer (or glass plate etc.) on which a photosensitive material is applied, an exposure apparatus such as a stationary exposure type (one-shot exposure type) projection exposure apparatus (so-called stepper) based on the step-and-repeat method and a scanning exposure-type projection exposure apparatus (so-called scanning stepper) based on the step-and-scan method are used. These exposure apparatuses are provided with a reticle stage and a wafer stage for positioning and moving of the reticle and wafer, respectively.
In these stage systems, there are cases in which it is preferable that rigidity (bending rigidity) be as high as possible in order to obtain a high positioning accuracy. On the other hand, particularly in a reticle stage system of a scanning exposure type projection exposure apparatus, there are cases when weight saving in the moving portion is preferable or order to drive the moving portion at a high speed. Also, a weight saving in the stage system simplifies conveyance of the exposure apparatus, and is advantageous for lessening the burden on the plant where the exposure apparatus is to be installed.
When for example moving members in the stage system are made thin in order to lighten the stage system, difficulties related to manufacturing technology increase, which may lead to higher manufacturing costs. The bending rigidity and buckling strength of members made thin are inversely proportional to the cube of the thickness, and so fall by a large extent. In order to maintain the rigidity and strength at or above target values when reducing weight, provided the materials of the moving members of the stage system have the same specific rigidity (i.e., rigidity (coefficient of elasticity)/weight per unit volume), it is preferable to use materials having a low density. For example, art is disclosed of adopting a thinned structure or ribbed structure for moving members of a stage system in order to achieve further lightening after employing materials with as high a specific rigidity and low density as possible within a predetermined cost range (refer for example to PCT International Publication No. WO 2005/036618).
Recently large and heavy mirrors have been employed as a projection optical system of an exposure apparatus. In order to achieve a reduction in weight of such an exposure apparatus, weight saving in such a mirror is desired while maintaining a high degree of flatness of the reflecting surface.
A purpose of some aspects of the invention is to provide a stage apparatus and exposure apparatus that enables the achievement of a further weight reduction while scarcely lowering characteristics such as rigidity, strength, and degree of flatness.